The invention relates to an ultrasonic weld-resistant piezoelectric tone generator comprising a piezoelectric ceramic wafer bonded onto a metallic carrier plate, a process for producing it, and its installation in a piezo tone generator housing.
It is already known to produce piezoelectric tone generators by bonding a piezoelectric ceramic plate onto a metal plate.
In most applications, piezoelectric tone generators of the said type are installed in a housing in order to increase the achievable sound pressure level or to achieve a specific resonance behavior.
The installation generally takes place in this regard either by bonding-in or by clamping with the aid of spring washers. The washers can serve simultaneously for contacting, no special mechanical loads occurring in this case on the tone generator.
However, ultrasonic welding has proved to be a particularly rational and reliable production method in the case of the installation of plastic housings. In this process, two half-housings of plastic are fused together on their contact surfaces. The heat required is generated as friction heat at the interfaces by means of ultrasound. In the case of tone generator housings, the tone generator to be installed is simultaneously clamped during this process at its edge in the vicinity of the contact surfaces of the two half housings. In this process, it cannot be avoided that due to the vibrational energy applied to the plastic the tone generator is simultaneously excited to resonate and subjected in this way to a substantial load.
In tone generator elements produced according to the prior art, the ultrasonic welding leads in approx. 2% of cases to edge eruptions, cracks and thus to the functional incapacity of the piezoceramic.